import tkinter

window=tkinter.Tk()
window.title('my window')
window.geometry('400x300')
tkinter.Label(window,text='window上').pack()

frm=tkinter.Frame(window)
frm.pack()

frm_l=tkinter.Frame(frm)
frm_r=tkinter.Frame(frm)
frm_l.pack(side='left')
frm_r.pack(side='right')

tkinter.Label(frm_l,text='frml').pack()
tkinter.Label(frm_r,text='frmr').pack()
window.mainloop()